The present invention relates generally to suspension systems for vehicle seats, and more particularly to torsion bar suspension systems for seats used in trucks or off-the-road vehicles.
When a truck or off-the-road vehicle rides along a highway or moves across bumpy terrain, the driver or other seat occupants are bounced up and down in their seats. In a seat suspension system employing a torsion bar, the downward movement of the loaded or occupied seat acts against a resilient torsion bar which undergoes twisting in response to that downward movement. The torsion bar's natural resistance to being twisted provides the cushioning or spring action. The extent to which a torsion bar twists or gives depends upon the weight of the seat's occupant. Depending upon the weight or preferences of the seat's occupant, the torsion bar may give too much or too little. Therefore, it is desirable that a torsion bar suspension system be adjustable so that the torsion bar twists or gives in accordance with the particular weight or preference of the particular occupant of the seat at any given time. Adjustment of the torsion bar suspension system for this purpose is usually accomplished by preloading or pretwisting the torsion bar in a direction opposite to that in which it undergoes twisting in response to downward movement by an occupied seat.
It is also desirable that a torsion bar suspension system include seat-height adjusting structure to position the seat occupant at whatever height he prefers at any given time. However, such a height adjustment should be accomplished without changing the preload on the torsion bar, otherwise an occupant of the vehicle seat will have to adjust the preload every time he adjusts the height of the seat.
A prior art attempt to accomplish height adjustment without changing the preload in the torsion bar is disclosed in Lowe U.S. Pat. No. 3,774,963, but this prior art attempt employs a complicated structure involving a large number of parts.